// 第 N 个泰波那契数
//测试链接：https://leetcode.cn/problems/n-th-tribonacci-number/
public class Tribonacci {
    public int tribonacci(int n) {
        if(n==0) return 0;
        if(n==1 || n==2) return 1;

        int a = 0, b = 1, c = 1, d = 0;
        for(int i = 3; i <= n; i++) {
            d = a + b + c;
            //滚动数组优化空间复杂度
            a = b;
            b = c;
            c = d;
        }

        return d;
    }
}
